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Pharmaceuticals2026-06-11 · 11 min read

New World Screwworm in Texas: What Vet Practices Need to Know (2026)

USDA confirmed New World screwworm in Texas in June 2026. Here is what the parasite does, how to spot it, FDA-authorized treatments, and reporting obligations for veterinarians.

Ran Chen
Ran Chen
Founder, VetMedGuide. Life-sciences operator and 10× global market-access lead.
Published

On June 3, 2026, the USDA's Animal and Plant Health Inspection Service (APHIS) confirmed the detection of New World screwworm (Cochliomyia hominivorax) in a three-week-old calf in Zavala County, Texas. Within a week, at least six confirmed US cases had been reported — including the first known case in a dog and the first in a goat — across multiple Texas counties and into New Mexico.

The re-emergence ends decades of US eradication (aside from a localized outbreak in Key deer in Florida in 2016–2017). It also moves screwworm from a foreign-animal-disease textbook topic to a clinical reality for veterinarians practicing in or near the affected regions. The scale of the outbreak in Central America and Mexico has been historic: as of June 2026, more than 171,700 animal cases and over 2,070 confirmed human infestations have been recorded, including at least 10 fatalities, across the region. Here is what the evidence, the regulatory response, and the USDA playbook say about what veterinary teams need to know right now.

What Is New World Screwworm?

New World screwworm (NWS) is a parasitic fly whose larvae feed on the living tissue of warm-blooded animals. Unlike most maggots, which colonize dead or necrotic tissue, screwworm larvae burrow into healthy flesh, creating progressively enlarging wounds that can become fatal within a week if untreated.

The fly (Cochliomyia hominivorax) is native to the Americas. It was eradicated from the United States in 1966 through a sterile insect technique (SIT) program — one of the most successful pest-eradication campaigns in history. A brief re-emergence occurred in the Florida Keys in 2016–2017, when NWS was detected in endangered Key deer; that outbreak was eradicated by March 2017 using the same sterile fly technique. A physical and biological barrier was maintained at the Darién Gap in Panama for decades, but in late 2024 the pest was detected moving north through Mexico, reaching the US border.

Host range

NWS can infest any warm-blooded animal:

  • Livestock: Cattle, sheep, goats, swine, horses — the primary economic target
  • Companion animals: Dogs and cats, particularly those with outdoor access or existing wounds
  • Wildlife: Deer, wildlife species
  • Humans: Rare, but documented. Anyone with a suspicious lesion should seek immediate medical care

Timeline of the 2026 US Outbreak

Date Event
Late 2024 NWS detected moving north through Mexico
June 25, 2025 Texas governor announces New World Screwworm Response Team
August 15, 2025 USDA announces comprehensive eradication actions
February 9, 2026 USDA Secretary Rollins and Governor Abbott open sterile fly dispersal facility in Texas
June 3, 2026 First US case confirmed: 3-week-old calf, Zavala County, TX (umbilical area)
June 5, 2026 Second case confirmed: calf, Zavala County, TX
June 8, 2026 Third case: calf in La Salle County, TX
June 8, 2026 Fourth case: dog seen in Andrews County, TX (later reclassified as Lea County, NM — first case outside Texas)
June 8, 2026 Fifth case: goat in Gillespie County, TX — extends geographic reach beyond South Texas
June 9, 2026 Sixth case: calf, La Salle County, TX

The dog and goat cases are significant because they demonstrate that NWS is not confined to livestock operations or a single geographic cluster. The dog case, originally reported from Andrews County, was reclassified to Lea County, New Mexico, after investigation revealed the animal was from a household there. The goat in Gillespie County — over 200 miles from the South Texas cluster — further extends the geographic footprint.

Clinical Recognition: What to Look For

NWS should be suspected in any animal presenting with:

  • Draining or enlarging wounds that do not heal or worsen rapidly
  • Maggots or egg masses visible in or around wounds
  • Eggs laid in body openings: nose, ears, genitalia, umbilical area of newborns
  • Signs of discomfort disproportionate to visible wound size
  • Progressive tissue damage with a foul odor

Screwworm larvae are cream-colored, with one end wider than the other, and rows of dark spines around the body. They are typically found deep within wound tissue, not just on the surface. A key differentiator from other myiasis: screwworm larvae feed on living tissue, and the wound actively enlarges.

Common entry sites

  • Umbilical stump of newborns (the first Texas case was a calf with umbilical infestation)
  • Existing wounds, surgical incisions, or tick bites
  • Mucous membranes: nasal passages, ear canals, genitalia
  • Branding or castration wounds in livestock

Regulatory and Reporting Obligations

NWS is a reportable foreign animal disease in the United States. This means:

  1. Veterinarians must report suspected cases within 24 hours. In Texas, contact the Texas Animal Health Commission (TAHC) at 1-800-550-8242. Outside Texas, contact your USDA Area Veterinarian in Charge (AVIC) or state animal health official.

  2. Do not attempt to treat and release without reporting. A foreign animal disease investigation is triggered by the report, and APHIS will coordinate sample collection and official identification.

  3. Interstate movement restrictions are in effect. Arkansas and other states have already imposed entry requirements for animals from Texas, including an Interstate Certificate of Veterinary Inspection (ICVI) dated within 7 days of entry and a statement confirming the animal was "inspected and found free of evidence of NWS infestation."

  4. Quarantine zones have been established. USDA and TAHC are enforcing a 20-km infested zone around confirmed detections, with movement controls and surveillance.

The regulatory landscape is evolving rapidly. Veterinarians in affected states should check screwworm.gov and their state animal health commission daily for updated guidance.

Treatment Options

FDA Emergency Use Authorizations and Conditionally Approved Drugs

The FDA has issued Emergency Use Authorizations (EUAs) and conditional approvals covering treatment products for NWS in multiple species. These authorizations were issued ahead of the US detections and represent treatment options that did not exist a year ago. As of June 2026, FDA-authorized products include:

Companion animals (dogs and cats):

  • Credelio (lotilaner) — EUA for dogs
  • Credelio CAT (lotilaner) — EUA for cats
  • NexGard (afoxolaner) — EUA for dogs
  • NexGard COMBO (afoxolaner + esafoxolaner) — EUA for cats
  • Credelio Quattro-CA1 (lotilaner + moxidectin) — conditionally approved for dogs
  • Nitenpyram tablets — EUA for dogs and cats (≥ 2 lb, ≥ 4 weeks old)

Livestock and multi-species:

  • Dectomax / Dectomax-CA1 (doramectin) — EUA and conditional approval for cattle, including dairy cattle; also authorized for horses, swine, sheep, and deer
  • Exzolt Cattle-CA1 (fluralaner) — conditionally approved for cattle
  • Ivomec (ivermectin injectable) — EUA, over-the-counter for cattle
  • F10 Antiseptic Wound Spray with Insecticide (benzalkonium chloride, polyhexanide, cypermethrin) — EUA for cattle, horses, minor hoof stock, birds, and exotic/zoo mammals
  • F10 Antiseptic Barrier Ointment with Insecticide — EUA for cattle, sheep, goats, horses, wild and exotic mammals, wild and pet birds
  • Negasunt Powder (coumaphos, propoxur, sulfanilamide) — EUA for multiple species

Product names, dosing, and the full authorization status should be confirmed through the FDA's NWS drug information page and the FDA's Dear Veterinarian letter dated June 5, 2026, as these authorizations are evolving. The USDA National Veterinary Stockpile has relocated NWS treatment supplies to Texas, available through TAHC.

The key clinical point: treatment exists and should be initiated immediately in confirmed or strongly suspected cases, concurrent with the mandatory reporting process.

General treatment principles

  • Debride the wound. Remove larvae mechanically. Preserve specimens in 70% ethanol for official identification.
  • Apply approved larvicidal treatment to the wound and surrounding tissue.
  • Supportive care: Antibiotics for secondary bacterial infection, anti-inflammatory medications, fluid therapy as needed.
  • Monitor for reinfestation. Eggs can be laid in the same wound by additional flies.
  • Isolate the animal to prevent spread and protect the wound from further fly strike.

Left untreated, screwworm infestation can kill an animal within one week.

The Eradication Response

USDA is leading a coordinated response that includes:

  • 75+ personnel on the ground in Texas, with hundreds more providing laboratory, logistics, and operational support nationwide
  • Sterile insect technique (SIT): Over 4 million sterile flies released aerially per week in South Texas, with additional ground release chambers being deployed. The sterile males mate with wild females, producing no offspring and progressively collapsing the population.
  • Expanded trapping and surveillance along the border and outside the dispersal area
  • Wildlife surveillance and management through Texas Parks and Wildlife
  • National Veterinary Stockpile activated and ready to provide treatments, equipment, and logistics

USDA Secretary Rollins visited the Knipling-Bushland US Livestock Insects Research Laboratory in Kerrville, Texas, on June 9, 2026. President Trump appointed John Bellinger as Senior Advisor for New World Screwworm Preparedness.

What Veterinary Practices Should Do Now

If you practice in Texas or bordering states

  1. Add NWS to your differential for any animal presenting with a draining wound, maggots, or unexplained tissue damage.
  2. Educate your team. Ensure every veterinarian and technician can recognize screwworm larvae and knows the reporting number.
  3. Check animals before interstate transport. Movement restrictions are already in effect.
  4. Stock approved treatments. Confirm availability through your distributor and the USDA stockpile.
  5. Counsel clients with outdoor pets or livestock to check animals daily for wounds and fly strike.

If you practice elsewhere in the US

  1. Be aware, not alarmed. The current risk outside the affected area is low, but the geographic spread — from Zavala County to Gillespie County (over 200 miles) and into New Mexico — shows the pest can move well beyond localized clusters.
  2. Know the reporting pathway. Every state has a USDA AVIC and a state veterinarian. A suspected case anywhere in the US triggers the same federal investigation.
  3. Include NWS in travel history discussions. Clients who have moved animals from Texas or Mexico should be flagged.

Why This Matters Beyond Texas

The economic impact of a sustained NWS infestation would be severe. The US cattle industry is the most directly threatened, but the dog and goat cases confirm that companion animals and small ruminants are not exempt. The geographic spread — from South Texas to Gillespie County and into New Mexico — underscores how quickly the footprint can expand. The sterile fly program is proven and effective, but it requires sustained investment and time — the 1966 eradication took years.

For veterinary medicine, the 2026 re-emergence is a reminder that foreign animal diseases are not just a regulatory abstraction. They arrive in clinics, in patients, and in the urgent decisions practitioners make in real time.

Sources

Topics
Vaccination & Infectious DiseaseEmergency & Critical Care
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